A propelling nozzle with a variable contour can be used in subsonic, supersonic and hypersonic aircraft. The variable contour of the nozzle extends between opposite primary and secondary flaps which are sealingly guided over the surface of the walls of a nozzle housing. The primary and secondary flaps are pivotally hinged upstream and downstream, respectively, of the nozzle housing. In addition, the secondary flaps are pivotally hinged on pivots of the primary flaps arranged on the side remote from the jet issuing from the nozzle and are connected by curved sections to the primary flaps so as to form a continuous or level aerodynamic contour.